What Is Retinitis Pigmentosa?
Retina pigmentosa (RP) is a group of degenerative disorders of the retina. It is associated with the loss of the photoreceptor cells of the retina and pigment deposits in the retina's periphery. The human retina consists of two types of photoreceptor cells; rods and cones. Rods are linked to daytime vision, whereas cones are responsible for night vision. In a normal visual cycle, the light photons entering the eye are absorbed by the rods and cones of the retina. This, in turn, initiates vision.
Is Retinitis Pigmentosa Common?
It is the most common inheritable disorder of the retina, with one in every 4000 people getting affected by retinitis pigmentosa.
How Is Retinitis Pigmentosa Inherited?
Retinitis pigmentosa is inherited by a mendelian form of inheritance. There are three types of inheritance:
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Firstly, autosomal dominant. In this type of inheritance, one person from each generation is affected. However, the symptoms are mild.
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Secondly, an autosomal recessive type of inheritance is observed in some patients. It starts in the first decade of life and is milder.
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The disease can also be inherited through an X-linked inheritance pattern. This type of inheritance is associated with shortsightedness (myopia).
What Are the Different Forms of RP?
Retinitis pigmentosa is of two types. Based on the mode of the cause of the condition, it can be syndromic or non-syndromic.
What Causes Retinitis Pigmentosa?
Non-syndromic retinitis pigmentosa is caused due to the mutation of the genes coding for the photoreceptor cells of the retina. Cones are more commonly affected than rods. Hence night blindness is the first symptom of RP. The genes involved include RHO, NRL, ROM, and RP 1.
Syndromic retinitis pigmentosa most frequently occurs with several other syndromes. Diseases that are associated with retinitis pigmentosa include:
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Bardet Biedl syndrome.
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Metabolic diseases like Bietti’s disease, cystinosis, and homocystinuria.
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Neurological diseases such as Joubert syndrome and myotonic dystrophy.
What Is the Mechanism Involved Behind Photoreceptor Cell Death?
In humans, vision initiation is activated after light absorption by the rhodopsin protein in the photoreceptor cells. Rods consist of outer and inner segments; destruction of the outer segment causes destabilization of the protein. This, in turn, results in an increase in oxygen level and, ultimately, cell death due to oxygen toxicity.
Who Is Prone to Get Retinitis Pigmentosa?
Patients with a previous familial history are most prone to contracting the non-syndromic form of the disease. Patients suffering from certain syndromes, metabolic diseases, and neurological diseases are also at an increased risk of getting the syndromic forms of RP.
What Are the Clinical Presentations of Retinitis Pigmentosa?
RP can occur early in life, with the mid-stage symptoms presenting within two years, or it can be a late-onset disease where the first stage of the symptoms occurs only at the mid-age. Non-syndromic retinitis pigmentosa has a typical appearance.
The typical form of RP occurs in three stages.
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In the early stage, night blindness is the main symptom. It starts in adolescence with very mild peripheral visual defects that the patient often ignores.
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In the mid-stage, there is complete night blindness with difficulty in peripheral vision. Patients become sensitive to light (photophobia), and there is the presence of a pale color hue. Patients find it difficult to read.
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In the end stage, the patient's autonomy is totally impaired due to the loss of visual acuity and peripheral vision. Photophobia is intense.
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Scotomas or blind spots may be present from the initial stages of the disease.
How Long Does the Effects of RP Last?
RP is a long-lasting and slowly progressing disease, with its manifestations persisting for several decades.
What Are the Different Ways of Diagnosing RP?
RP is diagnosed clinically by detecting night blindness, peripheral visual defects, and lesions of the fundus (hollow part of the eyeball, opposite to pupil).
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Full-field ERG (electroretinogram) is the ideal choice for diagnosing the disease at the earliest stage. It shows variation in the electrical wave.
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The clinical appearance of the fundus is examined with the help of a fundoscopy. In the early stages, the fundus appears normal. In the mid and later stages of the disease, bone-spicule-shaped deposits are deposited in the retina's periphery.
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Visual acuity is also tested.
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Fluorescein angiography in the later stages reveals complete obstruction of the vessels with chorioretinal destruction or damage.
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Molecular testing is done to investigate the gene responsible for the disease. However, it is expensive.
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Antenatal diagnosis (pre-birth diagnosis) of the disease can be performed if there is a known familial history.
What Are the Diagnostic Criteria Used to Diagnose RP?
Before forming a confirmatory diagnosis of RP, the following criteria must be checked:
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Functional signs such as night blindness, photophobia, and a decrease in visual acuity should be present.
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Deterioration of the visual field with poor peripheral vision, scotomas, and tunnel vision must be present.
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Fundus examination must reveal bony spicule deposits, narrowing and ultimately blocking of the blood vessels, waxy pallor of the optic disc (the region where the retina connects with the optic nerve), and various levels of retinal destruction (atrophy).
How Is Retinitis Pigmentosa Managed?
At present, there is no treatment to completely eradicate the disease. The current treatment modalities are primarily aimed at slowing down the progression of the disease, preventing complications, and helping people cope with the psychological impact of RP.
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Light protection therapies and vitamin supplements slow down the degeneration process. The use of orange-colored glasses while going outside and administration of vitamins A and E helps in slowing down the disease progression.
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The most important complications of RP are cataracts and macular edema. The removal treats cataracts of the lens and its replacement. Acute cases of macular edema are treated with topical carbohydrase inhibitors.
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Cryotherapy and lasers are utilized in cases with the presence of large exudates in the peripheral retina.
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Blind patients need psychological counseling to cope with the devastating effects of the disease.
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Gene therapy is a relatively new field of therapy used to treat the cause of the disease.
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Pharmacological management is used in cases with a known cause of the disease.
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Neuroprotectors, growth factors, retinal prosthesis, and tissue transplantation are a few methods used to protect the photoreceptor cells and enhance the lost visual field. However, these treatment modalities are in the early stages of research.
How to Prevent RP?
RP, once inherited, can not be prevented. Antenatal diagnosis and genetic counseling help provide detailed information to the families about the condition.
What Are the Conditions That Are Similar to RP?
RP needs to be differentiated from several other conditions with similar manifestations, such as:
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Nondegenerative night blindness.
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Leber’s congenital amaurosis.
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Vitamin A deficiency.
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Choroidal dystrophies.
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Maculopathies.
What Are the Complications Associated With RP?
The most serious complication of RP is loss of the visual field. Other frequently occurring complications include:
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Cataract.
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Macular edema.
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Inflammatory exudates.
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Increase in intraocular pressure.
What Is the Prognosis of Retinitis Pigmentosa?
The prognosis of retinitis pigmentosa varies for each patient. It is based on the patient’s visual field, visual acuity, and contrast sensitivity.
Conclusion
Retinitis pigmentosa is the most common inherited pathology of the retina's photoreceptor cells. Initially presenting with night blindness, the disease progresses slowly to blindness. Early detection and initiation of appropriate treatment modalities help reduce its adverse effects.
